1. Field of the Invention
The present invention relates to a display device and to a method of manufacturing a transparent substrate for a display device. In particular, the present invention relates to a display device such as an organic EL (electroluminescent) element, a liquid crystal display device and a plasma display, and to a method of manufacturing a transparent substrate to be employed in these devices.
2. Description of the Related Art
A glass substrate, a transparent electrode and an organic film all constituting a display device such as an LCD, a PDP and an organic EL element are generally high in refractive index. As a result, there is a problem that due to the reflection of light by the surface of glass substrate or by the interface at the transparent electrode or the organic film, loss of light is caused to occur. Therefore, it is difficult to effectively retrieve or pick up the light that has been generated in the display device or that has been introduced into the display device.
Since the reflectance as measured from the display face side of the display device is 10 to 15% at the black matrix (BM) of the color filter portion disposed inside the display device and 3 to 5% at the interface between air atmosphere and the face of the display device, problems of reflection and glare are caused to occur.
With a view to solving the aforementioned problems, there have been employed a method wherein multiple layers of materials differing in refractive index from each other are formed as an anti reflection layer on the surface of a display device, and a method wherein a low refractive index material (1.35-1.4) consisting of a fluorine-based compound is coated on the surface of a display device. There is also proposed adopting a low reflection structure (Cr/CrOx or Mo/MoOx) as a material for constituting the BM portion, thereby making it possible to reduce the reflectance of the display device. However, although the aforementioned anti reflection layer consisting of multiple layers is excellent in terms of performance, it is difficult to control the film thickness, resulting in increase in manufacturing cost. On the other hand, the use of low refractive index materials is effective in reducing the reflectance to 2%, the effect of such a degree is not sufficient. Namely, as long as the BM portion is concerned, even if low refractive index materials are used for that, the reflectance thereof is as high as about 3%, which is still insufficient.
In an effort to enhance the light-retrieving efficiency or to minimize the reflectance, it is now being studied to apply a regular structure of nanometer size to the surface of a semiconductor or glass substrate to obtain a semiconductor or glass substrate which is high in transmittance and low in reflectance. However, since only a regular structure of nanometer size is capable of realizing such anti reflection effects, even the lithography using a latest excimer laser is barely capable of achieving such a fine regular structure. Therefore, in order to realize such a fine regular structure, it is required to use an electron beam and, by using the electron beam, to perform the drawing and etching for creating the aforementioned regular structure. The use of an electron beam however leads to an increase in manufacturing cost as well as to the deterioration of productivity, thus making this method impractical. Moreover, since the regular structure is required to be created in the order of nanometer size, there is little tolerance in the process involved.
Further, there is also known a surface roughening technique wherein the surface to be treated is treated using hydrochloric acid, sulfuric acid, hydrogen peroxide or a mixed solution containing any of these materials. This surface roughening technique however is accompanied with a problem that this technique is greatly influenced by the crystallinity of the substrate and hence the surface of the substrate can be roughened or cannot be roughened depending on the azimuth of the exposed surface thereof. Of course, in the case of amorphous materials such as glass, the surface roughening thereof is fundamentally impossible. Therefore, it is not always possible to achieve the surface-roughening, thus restricting the usefulness of this roughening technique to improving the light retrieving efficiency.